PROPYLENE RANDOM COPOLYMER FOR USE IN FILM APPLICATIONS

Abstract

The present invention is directed to a polypropylene composition (P) comprising a bimodal copolymer of propylene and 1-hexene prepared in the presence of a metallocene catalyst, said bimodal copolymer having a melt flow rate MFR2 in the range of 4.0 to 20.0 g/10 min. Further, the present invention is directed to a method for preparing the copolymer (C) and an article comprising said polypropylene composition (P).

Claims

1-17. (canceled)

18. A polypropylene composition (P), comprising at least 90.0 wt.-%, based on the overall weight of the polypropylene composition (P), of a copolymer (C) of propylene and 1-hexene, having i) an overall 1-hexene content in the range of 2.0 to 10.0 wt.-%, ii) a melt flow rate MFR.sub.2 determined according to ISO 1133 (2.16 kg, 230° C.) in the range of 4.0 to 20.0 g/10 min, and iii) an amount of 2,1 erythro regio-defects of at least 0.2 mol.-%, wherein the copolymer (C) has been visbroken with a visbreaking ratio (VR) in the range of 1.5 to 15.0, wherein the visbreaking is determined according to equation (2) $\begin{array}{cc}\mathrm{VR}=\frac{{\mathrm{MFR}}_{\mathrm{final}}}{{\mathrm{MFR}}_{\mathrm{start}}}& \left(2\right)\end{array}$ wherein “MFR.sub.final” is the melt flow rate MFR.sub.2 determined according to ISO 1133 (230° C., 2.16 kg) of the copolymer (C) after visbreaking and “MFR.sub.start” is the melt flow rate MFR.sub.2 determined according to ISO 1133 (230° C., 2.16 kg) of the copolymer (C) before visbreaking.

19. The polypropylene composition (P) according to claim 17, wherein the copolymer (C) has a xylene soluble content (XCS) of at least 8.0 wt.-%.

20. The polypropylene composition (P) according to claim 17, wherein the copolymer (C) comprises a) a first random propylene copolymer (A) of propylene and a 1-hexene having a comonomer content in the range of 0.1 to 4.0 wt.-%, and b) a second random propylene copolymer (B) of propylene and 1-hexene having a higher comonomer content than the first random propylene copolymer (A).

21. The polypropylene composition (P) according to claim 17, wherein the copolymer (C) has a 1-hexene content of the xylene soluble fraction C6(XCS) in the range of 2.0 to 15.0 wt.-%.

22. The polypropylene composition (P) according to claim 17, wherein the copolymer (C) comprises 30.0 to 70.0 wt.-% of the first random propylene copolymer (A) and 30.0 to 70.0 wt.-% of the second random propylene copolymer (B), based on the overall weight of the copolymer (C).

23. The polypropylene composition (P) according to claim 17, wherein the copolymer (C) has a melting temperature Tm below 140° C.

24. The polypropylene composition (P) according to claim 17, wherein the copolymer (C) fulfills in-equation (1) $\begin{array}{cc}4.50\le \frac{C6\left(C\right)}{C6\left(A\right)*\frac{\left[A\right]}{\left[C\right]}}\le 9.00& \left(1\right)\end{array}$ wherein C6(A) is the 1-hexene content of the first random propylene copolymer (A) based on the total weight of the first random propylene copolymer (A) [in wt.-%]; C6(C) is the 1-hexene content of the copolymer (C) based on the total weight of the copolymer (C) [in wt.-%]; and [A]/[C] is the weight ratio between the first random propylene copolymer (A) and the copolymer (C) [in g/g].

25. The polypropylene composition (P) according to claim 17, wherein the copolymer (C) has a melt flow rate MFR.sub.2 determined according to ISO 1133 (230° C., 2.16 kg) before visbreaking in the range of 0.4 to below 4.0 g/10 min.

26. The polypropylene composition (P) according to claim 17, wherein i) the first random propylene copolymer (A) has a melt flow rate MFR.sub.2 (230° C., 2.16 kg) determined according to ISO 1133 before visbreaking in the range of 0.3 to 6.0 g/10 min, and/or ii) the second random propylene copolymer (B) has a melt flow rate MFR.sub.2 (230° C., 2.16 kg) determined according to ISO 1133 before visbreaking in the range of 0.1 to 4.0 g/10 min.

27. A process for the preparation of a copolymer (C) of propylene and 1-hexene, comprising the steps of a) preparing a copolymer (C′) of propylene and 1-hexene having an overall 1-hexene content in the range of 2.0 to 10.0 wt.-% in the presence of a metallocene catalyst (MC), b) visbreaking the copolymer (C′) obtained in step a) with a visbreaking ratio (VR) in the range of 1.5 to 15.0, thereby obtaining the copolymer (C), wherein the visbreaking is determined according to equation (3) $\begin{array}{cc}\mathrm{VR}=\frac{\mathrm{MFR}\left(C\right)}{\mathrm{MFR}\left(C^{\prime }\right)}& \left(3\right)\end{array}$ wherein “MFR(C)” is the melt flow rate MFR.sub.2 determined according to ISO 1133 (230° C., 2.16 kg) of the copolymer (C) after visbreaking and “MFR(C′)” is the melt flow rate MFR.sub.2 determined according to ISO 1133 (230° C., 2.16 kg) of the copolymer (C′).

28. The process according to claim 27, wherein the copolymer (C′) of propylene and 1-hexene is prepared by a1) polymerizing propylene and 1-hexene in a first reactor (R-1) in the presence of the metallocene catalyst (MC), thereby obtaining a first random propylene copolymer (A) having a 1-hexene content in the range of 0.1 to 4.0 wt.-%, a2) transferring said first random propylene copolymer (A) and unreacted comonomers of the first reactor (R-1) in a second reactor (R-2), and a3) polymerizing in said second reactor (R-2) and in the presence of said first random propylene copolymer (A) propylene and 1-hexene obtaining a second random propylene copolymer (B) having a higher comonomer content than the first random propylene copolymer (A), said first random propylene copolymer (A) and said second random propylene copolymer (B) forming the copolymer (C′).

29. The process according to claim 27, wherein i) the melt flow rate MFR.sub.2 determined according to ISO 1133 (230° C., 2.16 kg) of the copolymer (C) is in the range of 4.0 to 20.0 g/10 min and ii) the melt flow rate MFR.sub.2 determined according to ISO 1133 (230° C., 2.16 kg) of the copolymer (C′) is in the range of 0.4 to below 4.0 g/10 min.

30. The process according to claim 27, wherein the metallocene catalyst (MC) is of formula (I)
R.sub.n(Cp).sub.2MX.sub.2  (I) wherein each Cp independently is an unsubstituted or substituted and/or fused cyclopentadienyl ligand, substituted or unsubstituted indenyl or substituted or unsubstituted fluorenyl ligand; the optional one or more substituent(s) being independently selected from the group consisting of halogen, hydrocarbyl, C.sub.3-C.sub.12-cycloalkyl which contains 1, 2, 3 or 4 heteroatom(s) in the ring moiety, C.sub.6-C.sub.20-heteroaryl, C.sub.1-C.sub.20-haloalkyl, —SiR″.sub.3, —OSiR″.sub.3, —SR″, —PR″.sub.2, OR″, and —NR″.sub.2, wherein each R″ is independently a hydrogen or hydrocarbyl selected from the group consisting of C.sub.1-C.sub.20-alkyl, C.sub.2-C.sub.20-alkenyl, C.sub.2-C.sub.20-alkynyl, C.sub.3-C.sub.12-cycloalkyl, and C.sub.6-C.sub.20-aryl; or in case of —NR″.sub.2, the two substituents R″ can form a five- or six-membered ring, together with the nitrogen atom to which they are attached; R is a bridge of 1-2 C-atoms and 0-2 heteroatoms, wherein the heteroatom(s) can be Si, Ge and/or O atom(s), wherein each of the bridge atoms may bear independently substituents selected from the group consisting of C.sub.1-C.sub.20-alkyl, tri(C.sub.1-C.sub.20-alkyl)silyl, tri(C.sub.1-C.sub.20-alkyl)siloxy and C.sub.6-C.sub.20-aryl substituents; or a bridge of one or two heteroatoms selected from silicon, germanium and oxygen atom(s), M is a transition metal of Group 4 selected from Zr or Hf; each X is independently a sigma-ligand selected from the group consisting of H, halogen, C.sub.1-C.sub.20-alkyl, C.sub.1-C.sub.20-alkoxy, C.sub.2-C.sub.20-alkenyl, C.sub.2-C.sub.20-alkynyl, C.sub.3-C.sub.12-cycloalkyl, C.sub.6-C.sub.20-aryl, C.sub.6-C.sub.20-aryloxy, C.sub.7-C.sub.20-arylalkyl, C.sub.7-C.sub.20-arylalkenyl, —SR″, —PR″.sub.3, —SiR″.sub.3, —OSiR″.sub.3, —NR″.sub.2 and —CH.sub.2—Y, wherein Y is C.sub.6-C.sub.20-aryl, C.sub.6-C.sub.20-heteroaryl, C.sub.1-C.sub.20-alkoxy, C.sub.6-C.sub.20-aryloxy, NR″.sub.2, —SR″, —PR″.sub.3, —SiR″.sub.3, or —OSiR″.sub.3; each of the above mentioned ring moieties alone or as a part of another moiety as the substituent for Cp, X, R″ or R can further be substituted with C.sub.1-C.sub.20-alkyl which may contain Si and/or O atoms; and n is 1 or 2.

31. The process according to claim 30, wherein the metallocene catalyst (MC) of formula (I) is an organo-zirconium compound of formula (II) or (II′) ##STR00004## wherein M is Zr; each X is a sigma ligand; L is a divalent bridge selected from the group consisting of —R′.sub.2C—, —R′.sub.2C—CR′.sub.2, —R′.sub.2Si—, —R′.sub.2Si—SiR′.sub.2—, and —R′.sub.2Ge—, wherein each R′ is independently a hydrogen atom, C.sub.1-C.sub.20 alkyl, C.sub.3-C.sub.10 cycloalkyl, tri(C.sub.1-C.sub.20-alkyl)silyl, C.sub.6-C.sub.20-aryl, or C.sub.7-C.sub.20 arylalkyl; each R.sup.2 or R.sup.2′ is a C.sub.1-C.sub.10 alkyl group; R.sup.5′ is a C.sub.1-C.sub.10 alkyl group or a Z′R.sup.3′ group; R.sup.6 is hydrogen or a C.sub.1-C.sub.10 alkyl group; R.sup.6′ is a C.sub.1-C.sub.10 alkyl group or a C.sub.6-C.sub.10 aryl group; R.sup.7 is hydrogen, a C.sub.1-C.sub.6 alkyl group or a ZR.sup.3 group; R.sup.7′ is hydrogen or a C.sub.1-C.sub.10 alkyl group; Z and Z′ are independently O or S; R.sup.3′ is a C.sub.1-C.sub.10 alkyl group, or a C.sub.6-C.sub.10 aryl group optionally substituted by one or more halogen groups; R.sup.3 is a C.sub.1-C.sub.10 alkyl group; each n is independently 0 to 4; and each R.sup.1 is independently a C.sub.1-C.sub.20 hydrocarbyl group.

32. A polypropylene composition (P), comprising at least 90 wt.-% of the copolymer (C) obtained according to the process according to claim 27.

33. An article comprising at least 90.0 wt.-% of the polypropylene composition (P) according to claim 17.

34. A method of preparing a multi-layer film comprising a sealing layer, the method comprising utilizing the article according to claim 33 as a sealing layer.

Description

2. EXAMPLES

Preparation of the Catalyst

[0298] The catalyst used in the inventive example IE is prepared as described in detail in WO 2015/011135 A1 (metallocene complex MCi with methylaluminoxane (MAO) and borate resulting in Catalyst 3 described in WO 2015/011135 A1) with the proviso that the surfactant is 2,3,3,3-tetrafluoro-2-(1,1,2,2,3,3,3-heptafluoropropoxy)-1-propanol. The metallocene complex (MCi in WO 2015/011135 A1) is prepared as described in WO 2013/007650 A1 (metallocene E2 in WO 2013/007650 A1).

[0299] The catalyst used in the comparative example CE2, which is identical to inventive example IE3 of EP 2 386 603 A1, is described in example 1 of EP 1 741 725 A1.

Preparation of the Polypropylene Composition (P)

[0300] The polypropylene composition (P) was prepared in a sequential process comprising a loop reactor and a gas phase reactor. The reaction conditions are summarized in Table 1. Table 2 contains the properties of the comparative and inventive examples.

[0301] The polypropylene composition (P) was visbroken in a twin-screw extruder using an appropriate amount of (tert.-butylperoxy)-2,5-dimethylhexane (Trigonox 101, distributed by Akzo Nobel, Netherlands) to achieve the target MFR.sub.2 as mentioned in Table 2.

TABLE-US-00001 TABLE 1 Preparation of the Polypropylene composition (P) IE CE2 Prepolymerization Temperature [° C.] 20 n.d. Catalyst feed [g/h] 2.5 n.d. TEAL/C3 [g/t] 0 n.d. C3 feed [kg/h] 60.9 n.d. H2 feed [g/h] 0.5 n.d. Residence time [h] 0.2 n.d. Loop (R1) Temperature [° C.] 70 n.d. Pressure [kPa] 5297 n.d. H2/C3 ratio [mol/kmol] 0.08 n.d. C6/C3 ratio [mol/kmol] 15.5 n.d. MFR.sub.2 [g/10 min] 1.9 1.1 XCS [wt.-%] 1.9 1.0 C6 [wt.-%] 1.7 0.0 Residence time [h] 0.5 n.d. Split [wt.-%] 42.5 38 GPR (R2) Temperature [° C.] 80 n.d. Pressure [kPa] 2406 n.d. H2/C3 ratio [mol/kmol] 0.3 n.d. C6/C3 ratio [mol/kmol] 8.7 n.d. C6 (GPR) [wt.-%] 6.9 7.6 MFR.sub.2 (GPR) [g/10 min] 1.1 27.5 Residence time [h] 2.6 n.d. Split [wt.-%] 57.5 62 MFR.sub.2 (before [g/10 min] 1.5 8.1 visbreaking) MFR(C)/MFR(A) [−] 0.74 7.4 XCS (before [wt.-%] 11.1 3.0 visbreaking) C6(XCS) [wt %] 7.4 n.d.

TABLE-US-00002 TABLE 2 Properties of the comparative and inventive examples IE CE1 CE2 MFR.sub.2 (after [g/10 min] 9.0 8.0 8.1 visbreaking) C6 [wt.-%] 5.0 0.0 4.7 Tm [° C.] 136 140 148 XCS [wt.-%] 11.0 10.0 3.0 C6 FDA [wt.-%] 0.8 2.0 1.2 1, 2e [mol-%] 0.46 0.0 n.d. CF film Thickness [μm] 50 50 100 SIT [° C.] 105 114 104 Tm − SIT [° C.] 31 26 34 HTF [N] 2.7 2.0 3.1 TM/MD [MPa] 434 434 495 TM/TD [MPa] 432 432 503 W.sub.tot (Dynatest) [J/mm] 26.0 15.0 n.d. Haze b.s. [%] 0.3 0.2 n.d. Haze a.s. [%] 0.6 15 n.d. CE1 is the commercial copolymer of propylene and 4.5 wt % ethylene RD208CF of Borealis having a melt flow rate of 8.0 g/10 min which is produced by visbreaking a reactor-grade PP based on a Ziegler-Natta type catalyst to achieve the target MFR.

[0302] As can be gathered from Table 2, the haze after sterilization of the inventive compositions having an amount of 2,1 erythro regio-defects above 0.2 mol-% is significantly lower than the corresponding value of the comparative example, while the tensile modulus remains on the same level.